The present invention is directed to a process of emulsifying alkenyl succinic anhydride (ASA) size and to an ASA size emulsion. Description of Related Art Alkenyl succinic anhydrides (ASA) are useful in the sizing of cellulosic materials. As described in U.S. Pat. No. 4,606,773 to Novak, ASA sizes generally are represented by the formula 
wherein R represents a dimethylene or trimethylene radical and R1 is a hydrophobic group which may be selected from alkyl, alkenyl, aralkyl, and aralkenyl. Because ASA sizes of this structure are not water soluble, it generally is necessary to emulsify the ASA size to provide a composition which permits adequate contact with cellulosic fibers. ASA size emulsions typically are made with anionic or cationic starches, cationic polymers such as diallyldimethyl ammonium chloride polymers, polyamides, etc., or blends of starches and synthetic cationic polymers.
One major drawback associated with presently available ASA size emulsions is their relative instability. Separation or breakage normally occurs within as little as 4-6 hours after the emulsion is made. The precipitate undesirably can form deposits on pumps and in piping and other equipment.
U.S. Pat. No. 4,606,773 to Novak describes emulsifying ASA size using a physical blend of a cationic co-polymer, such as acrylamide-dimethylaminoethylacrylate, acrylamide-diethylaminoethyl acrylate, acrylamide-dimethylaminoethylmethacrylate, or acrylamide-diallyldimethyl animonium chloride, and a cationic starch made from corn starch or potato starch. The blend is said to provide increased stability to the emulsion over the use of either the co-polymer or the starch alone.
It would be desirable to develop a method of emulsifying ASA size that provides an emulsion having increased stability compared to presently available emulsions. It also would be desirable to develop a more cost-effective method of emulsifying ASA size.
It has been found that alkenyl succinic anhydride (ASA) size emulsions made using a starch grafted cationic acrylanide co-polymer as an emulsification agent exhibit greater stability compared to presently available ASA size emulsions. An ASA size emulsion prepared in accordance with a preferred embodiment of the invention exhibits more than 24 hours of stability, even up to 7 days or more of stability. It also has been found that the starch grafted co-polymer is a more efficient emulsification agent for ASA size. As a result, less emulsification agent is needed to emulsify ASA size, thereby saving cost.
In accordance with one aspect of the invention, a process of emulsifying an alkenyl succinic anhydride (ASA) size comprises blending an alkenyl succinic anhydride and a starch grafted cationic acrylamide co-polymer under conditions sufficient to form an emulsion. The ASA size optionally contains a surfactant such as sodium dioctyl sulfosuccinate.
The emulsified ASA size made in accordance with the present invention can be used in the manufacture of paper, paperboard, and the like in accordance with methods well known to those skilled in the art.